Low-frequency waves in the Santa Barbara Channel observed by high-frequency radar

2004 ◽  
Vol 109 (C2) ◽  
Author(s):  
Edwin Beckenbach
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Santa Barbara Channel ◽  
Santa Barbara ◽  
High Frequency Radar ◽  
Low Frequency Waves

Preferential acceleration of heavy ions from thermal velocities

1968 ◽  
Vol 46 (10) ◽  
pp. S638-S641 ◽  
Author(s):  
D. B. Melrose
Keyword(s):  
Frequency Spectrum ◽  
High Frequency ◽  
Heavy Ions ◽  
Crab Nebula ◽  
Low Frequency ◽  
High Frequency Waves ◽  
Hydromagnetic Waves ◽  
The Crab Nebula ◽  
Low Frequency Waves

The acceleration of ions from thermal velocities is analyzed to determine conditions under which heavy ions can be preferentially accelerated. Two accelerating mechanisms involving high-and low-frequency hydromagnetic waves respectively are considered. Preferential acceleration of heavy ions occurs for high-frequency waves if the frequency spectrum falls off faster than (frequency)−1. For the low-frequency waves heavy ions are less effectively accelerated than lighter ions. However, very heavy ions can be preferentially accelerated, the abundances of the very heavy ions being enhanced by a factor Ai over the thermal abundances. Acceleration of ions in the envelope of the Crab nebula is considered as an example.

scholarly journals Propagation of high frequency waves in the quiet solar atmosphere

2008 ◽  
pp. 87-99 ◽  
Author(s):  
A. Andic
Keyword(s):  
Solar Atmosphere ◽  
High Frequency ◽  
Low Frequency ◽  
Magnetic Structures ◽  
Partial Heating ◽  
Fabry Perot ◽  
High Frequency Waves ◽  
Propagation Of Waves ◽  
The Waves ◽  
Low Frequency Waves

High-frequency waves (5 mHz to 20 mHz) have previously been suggested as a source of energy accounting for partial heating of the quiet solar atmosphere. The dynamics of previously detected high-frequency waves is analyzed here. Image sequences were taken by using the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Izana, Tenerife, with a Fabry-Perot spectrometer. The data were speckle reduced and analyzed with wavelets. Wavelet phase-difference analysis was performed to determine whether the waves propagate. We observed the propagation of waves in the frequency range 10 mHz to 13 mHz. We also observed propagation of low-frequency waves in the ranges where they are thought to be evanescent in the regions where magnetic structures are present.

scholarly journals Underwater noise mitigation in the Santa Barbara Channel through incentive-based vessel speed reduction

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Vanessa M. ZoBell ◽  
Kaitlin E. Frasier ◽  
Jessica A. Morten ◽  
Sean P. Hastings ◽  
Lindsey E. Peavey Reeves ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Noise ◽  
Underwater Noise ◽  
Santa Barbara Channel ◽  
Noise Mitigation ◽  
Santa Barbara ◽  
Speed Reduction ◽  
Sound Exposure ◽  
Exposure Levels ◽  
Vessel Speed

AbstractCommercial shipping is the dominant source of low-frequency noise in the ocean. It has been shown that the noise radiated by an individual vessel depends upon the vessel’s speed. This study quantified the reduction in source levels (SLs) and sound exposure levels (SELs) for ships participating in two variations of a vessel speed reduction (VSR) program. SLs and SELs of individual ships participating in the program between 2014 and 2017 were statistically lower than non-participating ships (p < 0.001). In the 2018 fleet-based program, there were statistical differences between the SLs and SELs of fleets that participated with varying degrees of cooperation. Significant reductions in SL and SEL relied on cooperation of 25% or more in slowing vessel speed. This analysis highlights how slowing vessel speed to 10 knots or less is an effective method in reducing underwater noise emitted from commercial ships.

First noise and teleseismic recordings on a new ocean bottom seismometer capsule

1984 ◽  
Vol 74 (3) ◽  
pp. 1043-1058
Author(s):  
William A. Prothero ◽  
William Schaecher
Keyword(s):  
Sea Water ◽  
Low Frequency ◽  
Deep Ocean ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Data Logging ◽  
Santa Barbara Channel ◽  
Noise Levels ◽  
Santa Barbara ◽  
Recording Time

Abstract An ocean bottom seismometer capsule designed specifically for the long-term monitoring of teleseisms has been designed and tested. An efficient triggering algorithm consisting of multiple high-pass filters effectively discriminates between locally generated earthquakes and noise, and teleseisms. During a 1-month deep ocean deployment west of the Santa Barbara Channel, a magnitude 5.9 earthquake at a distance of 76° was recorded, in addition to a number of regional events in the 300- to 450-km range. Noise levels were monitored by automatically recording data at intervals. Vertical noise levels were approximately 20 times greater than those recorded at quiet land sites, and horizontal noise levels were about 5 times greater than that. The instrument consists of a microprocessor-controlled data logging system in three parallel pressure tubes, joined by a common baseplate. Wires between the three tubes are contained within the baseplate. There are no external connectors which are exposed to sea water, allowing the deployment time to extend to 1 yr. Data are recorded on two Braemar cassette recorders with a capacity of 15 Mbits each, for a continuous recording time of approximately 43 hr. This is adequate for the expected data acquisition rate, given the robustness of the triggering algorithm. The sensors are Mark Products L4-C 1-Hz seismometers with useful extended low-frequency response to about 30-sec periods for earthquake signals. The three components are leveled with a mechanical gimbal arrangement. The instrument has been successfully deployed 3 times in the Santa Barbara Channel and deep ocean, and should prove extremely useful for extending teleseismic studies into the ocean.

Growth of low-frequency waves due to a photon beam in a magnetized electron–positron plasma

1997 ◽  
Vol 58 (2) ◽  
pp. 345-366 ◽  
Author(s):  
QINGHUAN LUO ◽  
D. B. MELROSE
Keyword(s):  
High Frequency ◽  
Random Phase ◽  
Low Frequency ◽  
Photon Beam ◽  
Radio Waves ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Pair Plasma ◽  
Electron Positron ◽  
Low Frequency Waves

The effect of a beam of radio waves of very high brightness passing through a cold, magnetized, electron–positron plasma is discussed. The properties of the natural wave modes in such a plasma are summarized, and approximate forms for the nonlinear response tensor are written down. Photon-beam-induced instabilities of low-frequency waves in the pair plasma are analysed in the random-phase approximation. When three-wave interactions involve two high-frequency waves in the same mode and a low-frequency wave in a different mode, wave–wave interactions are similar to wave–particle interactions in that photons act like particles that emit and absorb low-frequency waves. The absorption coefficients for various low-frequency waves due to a photon beam are evaluated. In a pure electron–positron plasma, photon-beam-induced instabilities can be effective only when either the high-frequency or the low-frequency waves are strongly modified by the magnetic field. The growth of the low-frequency waves is most effective when the high-frequency photon beam has a frequency close to the cyclotron frequency.

scholarly journals Association of Alfvén waves and proton cyclotron waves with electrostatic bipolar pulses: magnetic hole events observed by Polar

2004 ◽  
Vol 11 (2) ◽  
pp. 205-213 ◽  
Author(s):  
G. S. Lakhina ◽  
B. T. Tsurutani ◽  
J. Pickett
Keyword(s):  
Boundary Layer ◽  
Free Energy ◽  
High Frequency ◽  
Low Frequency ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Polar Cap ◽  
Electron Holes ◽  
Proton Cyclotron ◽  
Low Frequency Waves

Abstract. Two magnetic hole events observed by Polar on 20 May 1996 when it was in the polar cap/polar cusp boundary layer are studied. Low-frequency waves, consisting of nonlinear Alfvén waves and large amplitude (±14nT peak-to-peak) obliquely propagating proton cyclotron waves (with frequency f~0.6 to 0.7 fcp), accompanied by electric bipolar pulses (electron holes) and electron heating have been observed located within magnetic holes. It is shown that low-frequency waves can provide free energy to drive some high frequency instabilities which saturate by trapping electrons, thus, leading to the generation of electron holes.

The interaction of high-frequency and low-frequency waves in magnetized plasmas

1988 ◽  
Vol 39 (3) ◽  
pp. 369-384 ◽  
Author(s):  
I. V. Relke ◽  
A. M. Rubenchik
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Magnetized Plasmas ◽  
Magnetic Field Fluctuation ◽  
Hamiltonian Description ◽  
Frequency Wave ◽  
Magnetohydrodynamic Waves ◽  
Self Focusing ◽  
Low Frequency Waves

The interaction of high-frequency and low-frequency waves in magnetized plasmas is considered. The narrowness of high-frequency wave packets makes possible a concise Hamiltonian description of the problem. Some concrete problems are studied with the help of the derived equations. The competitive role of scattering in self-consistent density and magnetic-field fluctuation are considered. The self-focusing and solitons of potential plasma waves and magnetohydrodynamic waves are studied.

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